1. Field of the Invention
The present invention relates to a solid-state imaging device applied to, for example, a charge coupled device (CCD) sensor.
2. Description of the Related Art
Of solid-state imaging devices, a solid-state imaging device of a so-called vertical overflow drain system for draining an excessive charge at a light receiving portion toward a substrate is well known.
In the vertical overflow drain system solid-state imaging device, e.g., in a charge coupled device (CCD) type solid-state imaging device manufactured by employing an n-type semiconductor substrate as a substrate, a method of forming an overflow barrier region by high-energy ion implantation is employed in order to form a so-called overflow barrier deep inside a silicone substrate to thereby improve the sensitivity of the imaging device.
However, when the above method is employed, the overflow barrier can be formed in the silicone without its depth from the surface of the substrate up to about 5 .mu.m at maximum.
As one of other methods, there is a method of forming an overflow barrier region by heating a portion where ion is implanted and diffusing impurities therein. When this method is employed, it takes a long period of time to manufacture the solid-state imaging device and contamination in the diffusion or the like largely influences the solid-state imaging device, which deteriorates characteristics of the solid-state imaging device.
It is known that the solid-state imaging device manufactured by employing the p-type semiconductor substrate as a substrate has a sensitivity to a frequency region of near infrared rays.
However, since a photoelectric conversion region of a light receiving portion thereof is not all depleted, a modulation transfer function (MTF; which represents a resolution) in the near-infrared-ray region is not satisfactory and a large amount of smear and dark current and so on occur, there is then the problem that the characteristics of the above solid-state imaging device are inferior to those of a solid-state imaging device formed by employing an n-type semiconductor substrate as a substrate.